Development of Catalysts for Polymer Degradation and Their Application to Plastics Recycling and Hydrogen Production

H-镓硅酸盐、FSM-16负载氧化镓和H-硼硅酸盐已被开发用于聚烯烃的化学回收催化剂，通过降解成有用的石化原料。镓硅酸盐显示出高活性，用于降解低密度和高密度聚乙烯和聚丙烯联产氢气和芳烃，主要是苯、甲苯和二甲苯（BTX）。随着反应温度的升高，氢气和BTX的产率也随之增加，在500 ℃时，氢气和BTX的产率分别达到3wt%和55wt%以上。产物分布受待降解聚烯烃结构的影响很小。这可以通过涉及分解片段的频繁骨架异构化的机理来解释。当使用Ga/FSM-16作为催化剂时，获得了4.5wt%的高氢气产率，其值对应于聚烯烃中所含氢气摩尔数的32%，虽然芳烃的产率降低，因为它们在催化剂表面转化为碳质材料。硼硅酸盐被发现是一种催化剂，它可以将聚烯烃分解成较低分子量的烯烃。丙烯和丁烯是主要产物，其产率随反应温度的升高而增加，而烷烃和芳烃的产量有限。从三种聚烯烃的降解中观察到几乎相同的产物分布。这些结果表明，使用镓和硼催化剂的开发技术作为聚烯烃化学回收的新选择是非常有前途的。

H-gallosilicate, gallium oxide supported on FSM-16, and H-borosilicate have been developed as catalysts for chemical recycling of polyolefins by degradation into useful petrochemical feedstocks.The gallosilicate showed a high activity for the coproduction of hydrogen and aromatic hydrocarbons, mostly benzene, toluene, and xylenes (BTX), from the degradation of low- and high-density polyethylene and polypropylene. The hydrogen and BTX yields increased with reaction temperature and went up to over 3 and 55 wt% at 500 ℃, respectively. The product distribution was influenced little by the structure of the polyolefins to be degraded. This can be explained by a mechanism involving frequent skeletal isomerization of the decomposed fragments.A high hydrogen yield of 4.5 wt%, the value of which corresponds to 32 % of the moles of hydrogen being contained in the polyolefins, was obtained when Ga/FSM-16 was used as a catalyst, although the yield of aromatics was reduced because of their transformation into carbonaceous materials on the catalyst surface.H-borosilicate was found to be a catalyst that can break down polyolefins into lower molecular weight olefins. Propylene and butenes were the main products and their yields increased with reaction temperature, while paraffins and aromatics were obtained in limited amounts. Almost the same product distributions were observed from the degradation of the three polyolefins.These results indicate that the developed technologies using gallium and boron catalysts are highly promising as new options for chemical recycling of polyolefins.